1. Field of the Invention
The present invention relates to a contact device used for a sliding contact of conductors of electrical equipment such as a gas insulated switch gear.
2. Description of Related Art
FIG. 14 is a sectional view illustrative of a conventional contact device described, for example, in Japanese Unexamined Utility Model Publication No. 61-82367.
In the drawing, coaxially formed on the end of a first conductor 1 and the end of a second conductor 2, which are arranged to be opposed to each other, are a contact section 1a and a contact section 2a, respectively, which have smaller diameters. A tulip contact 4 composed of many contact pieces 3 radially arranged along the axis is secured by a screw 6 via a holding plate 5 onto the contact section 1a of the first conductor 1. The contact section 2a of the second conductor 2 is detachably and slidably connected to the open end of the tulip contact 4. Garter springs 7 are fitted, two each, into both ends of the tulip contact 4 from the end where the outer periphery is located. The garter springs 7 are composed of helical springs, the overall length of each of which is smaller than the circumference of the circle that is circumscribed with the contact pieces 3; they impart contact pressure between contact sections 3a, 3b of each contact piece 3 and the contact sections 1a, 2a.
On the inner wall of a cylindrical shield 8, two guide plates 9 lying between adjacent contact pieces 3 are symmetrically installed along the axis. Two fixing leaf springs 10 are mounted in positions which are 90 degrees shifted from the guide plates 9; they are bent into a trapezoid shape to press the outer peripheries of the contact pieces 3. The shield 8 is pushed in from the opened end of the tulip contact 4 secured to the contact section 1a so that the guide plates 9 are inserted between adjoining contact pieces 3. This causes the leaf springs 10 to be pushed and deformed by the contact pieces 3; the elastic force of the leaf springs 10 installs the shield 8 to the tulip contact 4 in such a manner that it covers the tulip contact 4.
In the conventional contact device thus configured, the tulip contact 4 is attached to the contact section 1a of the first conductor 1 and the contact section 2a of the second conductor 2 is inserted from the opened end of the tulip contact 4. The tightening force of the garter springs 7 ensures the electrical contact between the contact sections 1a, 2a of the first and second conductors 1, 2 and the contact sections 3a, 3b of the contact pieces 3. This allows current to flow between the first and second conductors 1, 2 through the tulip contact 4.
The guide plates 9 are provided between adjoining contact pieces 3 to prevent the contact pieces 3 from falling. The shield 8 covers the tulip contact 4, thereby easing the concentration of electric field strength attributable to the projections and depressions on the outer peripheral portions of the contact pieces 3 and the garter springs 7.
The conventional contact device is used for connecting conductors of electrical equipment such as a gas insulated switch gear; it can be disassembled for transportation and reassembled at a site, where it is used, to permit easy connection between conductors.
The contact section 2a of the second conductor 2 is configured so that it slidably moves along the axis with respect to the contact section 3b of the contact piece 3; therefore, even if the first and second conductors 1 and 2 develop a temperature difference due to the supply of current or a change in ambient temperature and consequently expand or shrink, the electrical connection between the first and second conductors is secured. Moreover, the contact device can also be applied to a movable contact in such applications as a breaker or a disconnecting switch wherein a conductor is slid against a contact to admit current.
The contact device thus configured is known as a tulip contact or a polygon contact.
Thus, the conventional contact device has the garter springs 7 provided on the outer peripheries of the contact pieces 3; therefore, the outside diameter of the shield 8, that is, the outside diameter of the contact device is larger than the outside diameters of the first and second conductors 1 and 2. This has been posing a problem in that the outside diameter of the contact device unavoidably becomes even larger especially when the outside diameters of the contact sections 1a and 2a are increased to expand the contact area for carrying large current. This has resulted in a problem in that, when the conventional contact device is used, for example, in a gas insulated switch gear where a conducting section is placed in a tank, the diameter of the tank inevitably becomes large to secure a sufficient insulation distance.
Furthermore, when using the contact device, which has the tulip contact, for an application involving large current, many contact pieces 3 must be arranged in parallel in order to increase the contact area. In the conventional contact device, since the contact pressure is imparted to the contact pieces 3 by the tightening force of the garter springs 7, as the number of the contact pieces 3 increases, the component force which works as the contact pressure accordingly decreases. For this reason, it has been necessary to increase the number of the garter springs 7 or to employ larger garter springs 7 for providing greater tightening force to secure sufficient contact pressure, presenting a problem of deteriorated assemblability and an increased size of the device. In addition, a small angular difference causes great variations in the component force working as the contact pressure. This has led to greater chance of contact failures.